While the Companions were partying, the Echoes were preparing to invade the Quarry. On Cain's orders, they had stopped antagonizing the other hunters and stealing kills, so instead, they decided to wait until after dark when everyone had gone back into the city to go all out and hunt.
The quarry was enormous, almost a square kilometer, and completely packed with the Crazed. They weren't coming from here, the Echoes had been watching for hours and none of them left, but a few dozen more had arrived, pushing and jostling for space to get down the ramp and into the quarry. That made them think their Ancient wasn't as incompetent as he seemed, he had sent them to a spot where they could find a real challenge and not just some under-leveled dungeon where the best they could hope for was a time trial against each other.